Vegetative buffer zones are often used as mitigation solutions to reduce pesticide transfer from agricultural fields towards surface water. They need to be correctly designed in order to be efficient, taking into account the soil, agronomic and climatic conditions of the site in which they are located. Buffer efficiency is closely linked to its ability to infiltrate incoming fluxes, so that the infiltrating capacity must be suited to the incoming surface runoff. Irstea has developed a guide combining different tools, in order to design site-specific buffer zones by modeling their efficiency to limit runoff. It is based on representative surface runoff events for the considered implantation site, given the local climate and the contributive area characteristics (slope, length, soil, soil occupation, humidity status -these three parameters determining the curve number, a parameter reflecting soil tendency to generate runoff-). The buffer size is then optimized, considering its own characteristics (soil, water table depth) and the desired efficiency level, thanks to the mechanistic vegetative filter strip model VFSMOD. However, this tool set application is not totally user friendly, partly because it needs detailed field knowledge and data, which are usually not easily available in practice. In order to improve the method operability, we applied the sizing method to a large set of virtual scenarios, selected to encompass a wide range of conditions. These simulations led to abacus included in a user-friendly web tool. Depending on the available information that the user can fill in concerning the upslope contributing area and the buffer zone’s characteristics, the tool provides optimal lengths for different representative rainfall events and contributive area lenghts. This tool can be used either to design new VFS, by exploring different scenarios, or to improve current existing VFS placements and sizing.